Travelling-wave tube



Oct. 3, 1961 H. GROENDIJK ET AL TRAVELLING-WAVE TUBE Filed Feb: 24. 1959 INVENTORF;

HENDR K GP-OEND JK ARli VEP-SNiL COPBJ+L 5 TUN S DE W T AGEN 3,003,078 TRAVELLING-WAVE TUBE Hendrik Groendijk, Arie Versnel, and Comelis Tennis De Wit, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Feb. 24, 1959, Ser. No. 795,024 Claims priority, application Netherlands Apr. 10, 1958 lClaim. (Cl. 315-35) The invention relates to a device comprising a travellingwave tube, of which the outer wall has a larger diameter at the area of the electron gun than at the area of the delay line, the input coupling being formed by a system of coaxial conductors, which system is coaxial to the tube. The invention furthermore relates to a travelling-wave tube intended for use in such a device.

The aforesaid devices give rise to the difiiculty that the diameters of the coaxial conductors, constituting the input coupling, must be very large, since the inner conductor must embrace the wall at the area of the electron gun. Since for the conventional impedances of coaxial conductors the ratio between the diameters of the two condoctors must have a definite value, the outer diameter is so large that the application of a magnetic focusing system brings about great difficulties.

The invention has for its object to provide a structure in which the diameters of the coaxial conductor system are at a minimum.

In accordance with the invention, in a device comprising a travelling-wave tube, of which the outer wall has a larger diameter at the area of the electron gun is provided with a metal layer from the cathode end to the other end of the gun, this layer being capacitatively coupled with the inner conductor of the coaxial system, the outer conductor having, at a certain distance from the gun, a gradually smaller diameter to assume approximately the outer diameter of the tube.

The structure according to the invention ensures in the first place that the inner conductor of the coaxial system need not embrace the electron gun, while at the area of the gun the ratio between the diameters of the metal layer and the outer conductor may be smaller than that between the outer conductor and the inner conductor, owing to the presence of the glass of the wall, which has a higher dielectric constant than air. Thus the diameter of the outer conductor is materially smaller than would be the case, when the inner conductor embraces the tube at the area of the electron gun.

The invention will be described more fully with reference to the accompanying drawing, which shows the gun end of the tube with the coupled system of conductors.

coaxial nited States Patent Referring to the figure, reference numeral 1 designates the glass wall of the travelling-wave tube, which has a comparatively small diameter at the area of the delay line 2. At the area of the gun 3 the portion 4 of the wall has a materially larger diameter. The cathode end 5 of the tube has a smaller diameter. From the tube foot 6, which holds a plurality of supply pins 7, the inner side of the glass wall is provided with a metal layer 8, which is coupled capacitatively at the narrow part with an inner conductor 9 of a system of coaxial conductors, of which 10 designates the outer conductor. After a detachable interruption 11 the outer conductor is prolonged in the portion 12, which merges gradually at 13 into a part of smaller diameter 14. The interruption 11 is provided to permitof slipping the tube into the parts 12 and 14. Owing to the capacitative coupling between 9 and 8, they constitute relative prolongations without troublesome refleotions, so that a signal introduced into the system 9, 10 reaches the end of the delay line 2 approximately without being attenuated.

What is claimed is:

A travelling-wave tube comprising an envelope, an electron gun structure within said envelope, said gun including a cathode, a delay line within said envelope and spaced from said electron gun, said envelope having a portion of given diameter surrounding the cathode and another portion having a diameter less than said given diameter surrounding the delay line, and an input coupling to said travelling-wave tube comprising a system of coaxial conductors, the inner conductor of said system comprising a first portion surrounding a portion of the envelope enclosing the cathode and a second portion comprising a metal layer on the inner wall of a portion of the envelope surrounding the electron gun, said first and second portions of said inner conductor being capacitatively coupled to one another, the diameter of said outer conductor decreasing gradually between the electron gun and the delay line until it has approximately the outer diameter of the envelope whereby at the area of the electron gun the ratio between the diameters of the metal layer and the outer conductor is smaller than the ratio between the diameters of the outer conductor and inner conductor.

References Cited in the file of this patent UNITED STATES PATENTS 2,5 57,961 

